Could a "Stealth Virus" Be Lurking?
From Infectious Disease Alert
Abstract & Commentary
By John F. Joseph, MD, FACP, FIDSA, FSHEA,
Associate Chief of Staff for Education, Ralph H.
Johnson Veterans Administration Medical Center;
Professor of Medicine, Medical University of South
Carolina, Charleston, is Associate Editor for
Infectious Disease Alert.
Dr. John is a consultant for Cubist, Genzyme, and
bioMerieux, and is on the speaker's bureau for
Cubist, GSK, Merck, Bayer, and Wyeth.
Source: Lombardi VC et al. Science. 8 October 2009
(10.1126/science. 1179052).
It has been known for years that patients with
chronic fatigue syndrome (CFS) have a defect in a
major antiviral pathway, the 2-5A/RNase L pathway.
The RNaseL produces non-specific viral cleavage and,
thus, protects us from many viral infections (innate
immunity).
Defects in this pathway not only lead to
susceptibility to viral infections but may also
increase our susceptibility to tumor development.
The RNaseL gene, called Human Prostate Cancer 1
(HPC1), has a variant R462Q related to a potential
etiologic agent of prostate cancer, a novel human
retrovirus, xenotropic murine leukemia virus (MuLV),
named XMRV.
So, it was by a bit of serendipity that a group of
workers headed by several from the Whittemore
Peterson Institute in Reno, Nevada, asked if XMRV
could be associated with CFS.
What led to any rationale connection between
prostate cancer and CFS is not clear, but the
question led to a series of experiments that
culminated in a very recent publication showing an
association between the presence of this retrovirus
in the peripheral blood mononuclear cells (PBMCs) of
patients with CFS.
We are dealing here with intricate science that surely
took these 13 scientists and a host of technicians
years to produce. Yet the paper contains astounding
findings that I'll try to summarize succinctly, for
besides the eight primary article pages from Science
Express, there are 18 additional pages of
"supporting" materials that also contain fascinating
data.
Here is what the paper reports.
In 101 banked samples of PBMCs, 67% (68) were
positive for a XMRV gag sequence. Next, seven of 11
PBMC CFS samples held at the Cleveland Clinic were
shown to have XMRV gag plus env. Only 3.7% of
PBMC DNA from healthy controls had XMRV gag when
tested by PCR.
Amazingly, those gag and env sequences were nearly
identical to those from XMRV from prostate
cancer-associated strains (PLoS Pathol.
2006;2:211).
Full-length SMRV from two patients differed from
prostate cancer strain VP62 by only six nucleotides,
showing again a > 99% identity between the CFS
and prostate cancer XMRV.
A phylogenetic comparison of six isolates from
CFS/Prostate cancer showed them to be significantly
different from other murine leukemic viruses.
In all, 50 other isolates of MLV were used to make
the neighbor-joining trees. The suspected closest
relatives were other xenotropic murine viruses (Xmv
15-19 and Xmv 10, 13, 16) and polytropic (Pmv) plus
modified polytropic (Mmpv) viruses, which were in
fact very removed genetically from XMRV.
Next, it was shown that several antibodies with
"novel viral specificities" all reacted with VP62 XMRV
proteins when grown in several cell lines, including a
line called LNCaP of prostate cells that are known to
permit infection with MXRV.
Flow cytometry of activated lymphocytes also
showed that 19 of 30 PBMC CFS samples reacted
with antibodies to MLV P30 Gag and other MLV
proteins whereas PBMCs from normal patients were
negative, for an odds ratio of 54.1. (confidence
intervals of 23.8-122).
So, there is a non-random association of CFS PBMCs
with XMRV. Both activated T and B cells from CFS
were infected with XMRV.
The next experiment was quite ingenious. PBMCs
from CFS patients were co-cultured with LNCaP cells,
the ones defective in RNaseL pathways.
The LNCaP cells became infected, as shown by
presence of XMRV gag and env proteins and by the
presence of whole virus, as seen by electron
microscope both at the time of infection and upon
release. The electron micrographs are quite
stunning.
The same type of infectivity was also seen when only
plasma from CFS patients was applied to LNCaP
cells. Thus, cell-associated and cell-free virus seems
to be infectious, at least to some cell lines.
Finally, it was shown that 50% of plasma samples
from patients with CFS have a humoral response to
XMRV, demonstrated by presence in flow cytometry
assays of antibodies to a viral env closely related to
XMRV env.
Commentary
It was courageous of Science to publish this paper
because there are obvious epidemiologic data
missing from the report.
Still, patients with CFS can clearly see from this
article the sophistication and dedication of scientists
studying CFS, giving them hope that there will be
some etiologies discovered in the near future.
Indeed, when Robert Suhadolnik and colleagues at
Temple University School of Medicine described the
defects in RNaseL in the mid 1990s, the newer
methods in retrovirology were just emerging so, in a
sense, these new studies had to await the
sophistication that has come with laboratory
advances in the HIV/AIDS era. Good science
(methodology) begets better science.
Esteemed Professors John M. Coffin and Jonathan P.
Stoye of Tufts University wrote an accompanying
editorial in the issue of Science Express.
They emphasize that the gammaretroviruses of mice,
including endogenous MLVs, have given us much
understanding of cancer pathogenesis; no such
association has been made in humans until XMRV
was discovered in prostate cancer tissue only three
years ago.
This work will have its critics. One concern is
laboratory contamination with MLV.
It is very unlikely that laboratory contamination freed
the XMRV into human cell lines. CFS PBMCs and
prostate cancer patients come from very disparate
backgrounds.
Indeed, the patients at the Whittemore Peterson
Institute also come from diverse geographies and,
except for their common diagnosis of CFS, have little
in common.
That fact makes it even more remarkable that out of
nearly 8000 nucleotides in XMRV-a retrovirus only
about 30 show variation.
That lack of genetic variation for XMRV lies in great
contrast to the huge variation we are used to seeing
in HIV, suggesting that XMRV has recently
descended from a common ancestor.
Drs. Coffin and Stoye in their editorial also focus on
the 3.7% of XMRV positivity in normal PBMCs and
non-cancerous prostate tissue. If this rate were to
hold up in studies from other geographic regions of
the world, that would suggest that at least 10
million people worldwide harbor the virus and
perhaps are more susceptible to a wide variety of full
expression of the retroviral infection.
As one of a group of physicians who has recognized
and managed patients with CFS for many years, my
bias is to believe the validity of these current data.
Yet, many theories about the cause of CFS have
come and gone. CFS patients are always looking for
new hope.
Indeed, an article in the New York Times of October
13 by Denise Grady speaks to thousands of patients
already clamoring to be tested for the new virus.
Of note also is that the Whittemore Peterson
Institute was founded by parents of a young woman
with CFS, so the data from Whittemore need to be
verified in additional cohorts of CFS patients.
Nevertheless, the passion of physicians like Dan
Peterson himself, and others in that kindred, has
driven the science of CFS.
Steadfast organizations like our national CFS
foundation, CFIDS (
www.cfids.org) , and many state
CFS organizations continue to sponsor patients and
programs that demand a balanced scientific playing
field which in part has led to the quality of work
demonstrated in the paper by Lombardi et al.
